1. Field of the Invention
The invention relates to electrical machines, and, more particularly, to contactless superconducting synchronous electrical machines used as synchronous generators and synchronous compensating devices.
2. Description of the Prior Art
Known in the art is a superconducting synchronous electrical machine which is a synchronous generator comprising a superconducting field winding cooled with helium at 4.degree. to 5.degree. K. (cf. the FRG patent application No. 2,028,158, cl. 21d.sub.2 -1 as published for opposition, 1971). The described machine also comprises a stator having a winding of non-superconducting material, a rotor implemented as a cryostat mounted on a shaft and accommodating the superconducting field winding, a means adapted to supply the cryostat with the coolant, bearings in which the shaft provided with vacuum-tight packings is rotatably mounted, a stationary dielectric casing surrounding the rotatable cryostat, and a contact means having a system of power leads through which the current from a stationary exciter is fed to the field winding.
Proper excitation of the described machine is attained by the use of internally stabilized superconducting winding materials which possess higher current-carrying capability in the presence of magnetic fields of great induction. As a result, the contact means with a system of power leads and the stationary exciter feature complex design and the machine has poor reliability and inadequate power characteristics.
There is a contactless superconducting synchronous electrical machine in which a superconducting field winding takes power from a superconducting exciter working as a magnetic flux pump (cf. the FRG patent application No. 1,488,730, cl.21d.sub.1 -51 as published for opposition, 1969).
The machine has an annular stator and a rotor with a superconducting field winding, fixed on rotatable shaft in a concentrical relation to the stator. The superconducting field winding is mounted in a main cryostat and is coupled to a superconducting armature winding of the exciter made of a thin sheet in the form of a disc and positioned in an additional cryostat, on the end face portion of the rotor shaft. The inductor of the exciter is rotated by an electric motor which is set in coaxial relation to the rotor shaft. The coolant is led to and withdrawn from the cryostat by virtue of a radially located coolant supply assembly. The rotatable shaft is set in stand-mounted bearings and the bearings on the exciter side is installed between the main and the additional cryostats.
In the described machine the availability of the electric motor for the exciter inductor makes it impossible to utilize an axially positioned coolant supply assembly which has the simplest design and operational features. As a result, the machine becomes complex and its reliability is poor. Moreover, greater design complexity is due to the fact that no stand-mounted bearing can be installed on the exciter side, in the vicinity of the end face of the shaft. Therefore, two cryostats, main and additional, must be used, with the result that it is impossible to install a single stationary dielectric casing surrounding the movable parts of the machine. In this casing, a vacuum is created and heat loss due to the rotation of the movable parts is thus reduced.